for the Microscope. 31 



215. COMMON AMPHIPLEURA (Amphipleura pdlucida). 

 The frustules are free and elongated, narrowly spear- 

 shaped, with longitudinal ridges. More or less common 

 in every wayside pool and rivulet. (PI. III., fig. 33.) 



216. LONG SYNEDRA (Synedra ulna). The frustules in 

 Synedra are elongated, and at first attached by the lower 

 end. In this species the sides of the valves are nearly 

 parallel, with the extremities suddenly pointed. Very 

 common. (PI. IV., fig. 33.) 



217. HEADED SYNEDRA (Synedra capitatd). The 

 valves are long and narrow, with parallel sides, expanding 

 at each end into a triangular head. Very common. (PI. 

 HI, fig. 35.) 



218. SLIPPER CYMATOPLEURA (Cymatopleura solea). 

 The frustules in this genus are oblong, the undulations of 

 the valves have a boss-like appearance on the margin, and 

 the surface of the valves undulated. The valves in this 

 species are narrow, gradually constricted towards the centre, 

 and the ends pointed, with six undulations, and the surface 

 striated. 



219. ELLIPTIC CYMATOPLEURA (Cymatopleura elliptica). 

 The valves are broadly elliptical, a little pointed at the 

 extremities, with four or five undulations ; the striae on the 

 surface not so distinct. Both species common in ditches. 

 (PL IV, fig. i.) 



220. TWO-ROWED SURIRELLA (Surirella biseriata). 

 In this genus the frustules are usually somewhat wedge- 

 shaped, the margins produced into a kind of wing, with 

 distinct, usually parallel, channels. The valves in this 

 species are broadly spear-shaped (elliptical lanceolate), 

 with conspicuous wings and large channels. 



221. NARROW SURIRELLA (Surirella linearis). Valves 

 narrower than in the last, occasionally constricted, with 

 either blunt or pointed extremities. Both species common 

 on marshes and ditches. (PI. Ill, fig. 36.) 



222. OVATE SURIRELLA (Surirella ovata). A minute 

 species. The valves ovate, wings small, and channels only 

 at the margins. The three preceding species will generally 

 be found in boggy pools. (PI. IV., fig. 34.) 



